1. Technical Field of the Invention
The present invention relates to improvement of an AC electric rotating machine with a stator in which multiphase stator coils are wound.
2. Description of the Related Art
One example of an AC (alternating current) electric rotating machine is proposed in Japanese Patent Publication (laid open) No. 2004-88993. For the AC electric rotating machine disclosed in this patent publication, a stator coil as described below is shown. In this example, the stator coil has a structure which is formed by a sequential process as follows. The process uses a U-shaped conductor (hereafter also referred to as a long U-shaped segment) which has a pair of long leg portions which extend in parallel with and separated from each other by a distance equivalent to the electric angle π (pi: a single magnetic pole pitch). The processing includes displacing the U-shaped conductor in a direction (i.e., the circumferential direction or the tangential direction when the stator core is installed) which is perpendicular to the direction in which the leg portions extend (i.e., the axial direction when the stator core is installed) by one magnetic pole pitch at a predetermined position from the side of a U-shaped head portion, and subsequently turning back the U-shaped conductor in the direction in which the leg portions extend. In this structure, a developed coil is configured having a shape in which a wave winding (also referred to as wave phase winding) equivalent to one phase has been developed. The developed coil is rounded into a cylindrical shape whereby the wave phase winding is formed. Next, the wave phase windings with the necessary number of phases are arranged in a state in which the wave phase windings are displaced from each other in the circumferential direction by a predetermined pitch which is equivalent to the inter-phase electric angle, whereby a cylindrical multi-phase stator coil is formed. Next, the multi-phase stator coil is pressed to the inside of each slot through an opening of each slot (also referred to as a slot opening) which is opened inwards in the radial direction of the stator core. The stator coil manufactured with the art will be hereafter referred to as a turning-back stator coil. Note that the turning-back as described above does not mean that the coil is not turned back as if it is folded up or down, but it means that the coil is turned back as if the coil wraps around a plate.
The stator coil will now be further described. One turn of the stator coil includes a pair of slot conductor portions and a pair of bridging portions. The pair of slot conductor portions are housed in a predetermined conductor housing position in the radial direction (also referred to as “layer” in the present specification) in the slot, and are separated from each other by substantially one magnetic pole pitch. The pair of bridging portions connect the pair of slot conductor portions which are separated from each other by substantially one magnetic pole pitch outside the slot. The turning-back stator coil has a single same-layer bridging portion and bridging portions (also referred to as different-layer bridging portions). The same-layer bridging portion connects in series the slot conductor portions which are at the same position in the radial direction (referred to as same layer) of two slots which are separated from each other corresponding to the magnetic pole pitch of NS poles of a rotor. Each bridging portion connects in series the slot conductor portions which are at different positions in the radial direction (referred to as different layers) of two slots which are separated from each other corresponding to the magnetic pole pitch of NS poles of a rotor. Each bridging portion forms a coil end on either opposite end in the axial direction of a stator core.
Further, a stator coil which is similar to the above-mentioned turning-back stator coil in the foregoing Japanese Patent Publication (laid open) No. 2004-88993 is disclosed in U.S. Pat. No. 6,930,426 and Japanese Patent No. 3476416.
However, Japanese Patent No. 3476416 describes a drawback in that both end portions must be connected to each other after the developed coil is wound around the stator in the layered state.
In addition, U.S. Pat. No. 6,930,426 describes a drawback in that the size of the coil end is increased since the coil is wound by merely meandering winding. Furthermore, Japanese Patent Publication (laid open) No. 2004-88993 describes a drawback in that the size of the connecting portion is increased. Furthermore, at least one of the same-layer bridging portion is provided for each phase and extends in the circumferential direction for connecting a pair of in-slot conductors in the same layer, which may cause spatial interference with other bridging portions which are adjacent thereto. Accordingly, the same-layer bridging portion and the other bridging portion which is adjacent thereto are bent inwards in the radial direction by a large amount to avoid the above-mentioned spatial interference. However, bending of the bridging portion inwards in the radial direction by a large amount creates a new problem with spatial interference between the bridging portion and an outer peripheral surface of the rotor. As a result of this, problems such as difficult designing and complicated operation in inserting the rotor in the stator are also created.